The present invention relates to a locknut for securing a threaded fitting and the like to a workpiece, or to a housing, particularly for electrical or electronic connections and/or equipment.
One known type of locknut used for connecting threaded fittings and threaded conduits to housings such as electrical junction boxes comprises a generally cylindrical portion having a multiple-turn thread helically extending interiorly of the cylindrical portion and spaced teeth or ears having portions projecting axially and radially outwardly of the cylindrical portion. The teeth are configured so that their radially extending portions can be impacted by the tip of a screwdriver or like implement when the locknut is threaded to the fitting or conduit to tighten the locknut against a housing. The teeth are further configured and of such hardness that their axially projecting portions may cut into the surface of the housing as the locknut is tightened against the housing to help provide good electrical contact between the locknut and the housing. The teeth can exhibit a limited degree of flexing in the axial direction as the locknut is tightened against the housing, which can provide a spring action capable of compensating by spring recovery for a slight loosening of the locknut.
Another known type of locknut is similar to the one described above in that it includes a cylindrical portion having a multiple-turn thread and radially extending ears. The ears are configured so that they can be impacted by the tip of a screwdriver or like element for tightening the locknut against a housing. However, the ears do no project axially beyond the end of the locknut. Instead, teeth in the form of a multiplicity of small ridges are disposed on an end face of the locknut projecting axially therefrom.
Still another known type of locknut is made of relatively thin sheet material and has a single-turn thread formed by bending the thin sheet material surrounding the central opening of the locknut. In order to mold the thin sheet material into a thread helix, the periphery of the central opening is slit at at least one place and bent one way and the other way either side of the slit to form the helix. Although such locknuts can be used with fittings having standard threads as defined hereinafter because the thread helices of the locknut and fitting may be matched approximately, locking characteristics are not particularly good because the parallel flanks of the locknut thread make contact with the converging flanks of the standard thread only along lines, as opposed to surfaces when both the locknut thread and the fitting thread are standard.
As used herein, "standard thread" refers to one in which the flanks of the thread converge towards the crest of the thread and form an included angle therebetween of from about 29.degree. to about 60.degree..